AND I. BERTINI 1520 L. SACCONI
Inorganic Chemistry CONTRIBUTION
CHIMICA GEXERALE E ISORGASICA, UNIVERSIT~ DI FIRENZE, FLORENCE, ITALY
FROM THE ISTITUTO D I
Complexes of Copper(I1) with Schiff Bases Formed from Salicylaldehydes and N- Substituted Ethylenediamines BY L. SACCON1
ASD
I. BERTINI
Received iWarch 28, 1966 Schiff bases, derived from ring-substituted salicylaldehydes and X-substituted ethylenediamines, form two series of compounds with copper(II), i.e., [ X - S A L ~ ~ - N ( R ) R ’ ] ~ C ( IU) and ~ ~ [X-SXLen-K(R)R’] CuY (11), where Y = C1, Br, CHBCOO. The complexes of type I have distorted trans-planar configurations, when R = H or CH3, R’ = C&, and R = R ’ = CsHs or CsHj. When R = H or CHI and R’ = CHI, howevcr, they probably have pentacoordinate configurations. In complexes with formula I1 only one Schiff base, which acts as a tridentate ligand, is linked to the copper(II), while the fourth coordination position is occupied by the halogen or the acetate group. The chloro complexes are also formed by dechlorination of solvents like CHCla or CC14.
Introduction Nickel(I1) and cobalt(I1) complexes with Schiff bases, formed from salicylaldehydes and N-substituted ethylenediamines of the general formula [X-SALen-N(RP’I
have been described in previous papers. 1--3 According to the steric requirements and the electronic properties of R, R’, and X , bases of this type behave in a bidentate or tridentate manner. In the bidentate case tetracoordinate complexes are formed (planar with Ni(I1) and tetrahedral with Co(II)), while in the tridentate case the complexes are octahedral. In particular cases, pentacoordinate complexes are formed in which one base functions in a bidentate and the other in a tridentate manner.2 Copper(I1) complexes of these ligands are reported in this paper. Two types of complexes have been obtained and characterized : one has the general formula [X-SALen-N(R)R’]&u” (I), and the other is of the type [X-SALen-N(R)R’]CuY (11),with Y = C1, Br, CH3CO0. Their structure has been elucidated by recording visible absorption and reflectance spectra and measuring the dipole moments of some characteristic compounds. Experimental Section Preparation of the Compounds.-The [X-SALen-N(R)R’] 2CUI’ (I) complexes, listed in Table I, have been prepared by heating the complexes bis(X-salicylaldehyde)copper(II) (10 mmoles) dissolved together with the appropriate N-substituted ethylenediamines (22 mmoles) in ethanol (ca. 50 ml) under reflux, until precipitation took place. I n some cases a little water was added to facilitate the precipitation. After cooling the reaction mixture, the precipitate mas filtered off and recrystallized (1) L. Sacconi, P. Nannelli, and U. Campigli, I ~ z o uChem., ~. 4, 818 (1965). ( 2 ) L. Sacconi, P. h-annelli, K. S a r d i , and U. Campigli, zbzd , 4, 943 (1965).
(3) L. Sacconi, &I. Ciampolini, and G. P. Speroni, z b i d . , 4, 1116 (1965).
from benzene-petroleum ether (bp 40-70’) solution. The conipounds of general formula 11, (X-SALen-N(R)R’] CuC1, with the exception of R = CH3 or CsHj and R’ = CsHs derivatives, have been prepared in two ways: (1) Work was performed as above but in chlorine-containing solvents such as CHC13 or CC14 rather than in ethanol. After cooling under reflux for 0.5 hr, the solution was concentrated until precipitation began. In some cases cyclohexane or petroleum ether was added to assist precipitation. After cooling, the precipitate was filtered and recrystallized from methanol or ethanol. The same result is obtained by heating and rccrystallizing the corresponding complexes of series I in CHCla or CCL. (2) The Schiff bases were mixed with an alcoholic solution, containing an equimolecular proportion of CuC12. Crystals were obtained by evaporation of the solvents, filtered off, and recrystallized as above. All attempts to prepare complexes of this type in which R = CH3 or CsHj and R‘ = C6Hs were unsuccessful. The complexes [SALen-N(H)CH3]CuBr and [SALen-K(H)CH3] CuCH3COO were obtained by the second method using CuBrn and Cu(CHBCOO)~, respectively. The analytical data for the most typical of these compounds are summarized in Table I. Spectrophotometric Measurements.-The absorption spectra were recorded with a Beckrnan DK2 spectrophotometer. The solvents were purified by the standard procedures used for spectrophotometric measurements. The reflectance spectra were recorded using the standard Beckman reflectance attachment and magnesium oxide as a reference. Concentrations of the solutions were in the range 0.01-0.02 M. Dielectric Polarization Measurements.-The apparatus and the procedures used have been previously described.4 The molar refraction for the sodium D line, RD, of the complexes was calculated by adding the proper values of bond refractions to the measured molar refraction of the bis(N-mcthylsalicylaldimino)nickel(II) ~ o m p l e x . ~Values of the orientation polarization, P o , were calculated by assuming a value of 207; RD for the atom polarization.
Results and Discussion Series I : [X-SALen-N(R)R’],Cu“.-The compounds in which R = CH3 or CSHSand R’ = C6H5 give reflectance spectra, with a single absorption band a t ca. 15,000 cm-l, which are similar to those of the distorted trans-planar bis(N-methylsalicyla1dirninato)copper(I1) complexe~.~ The corresponding ligands also act in a bidentate manner with Ni(II)l and C O ( I I ) , ~ (4) L. Sacconi, M. Ciampolini, F. Maggio, and F. P. Cavasino, J . Inorg. S z ~ r l Chem., . 19,73 (1961). ( 5 ) L. Sacconi, P. Paoletti, and G. Del Re, J . Am. Chem. Soc., 79, 4062
(1957).
Vol. 5, No. 9, September 1966 SUMMARY
OF
COMPLEXES OF COPPER(II) WITH SCHIFF BASES 1521
PHYSICAL
TABLE I ANALYTICAL DATAFOR SOME[X---SALen-N(R)R'I2CuII [X-SALen-N(R)R'] CuY COMPLEXES
AND
P
cu
MP, 'C
a
[5-Cl-SALen-N( H)CHa]2Cu [ SALen-N( CHs)2]ZCU [5-Cl-SALen-N( C Z H ~ )ZCU Z] [SALen-N( H)C&€5]2Cu [SALen-N( CH3)CeHj]2Cu [SALen-N( CsHs)z]ZCU [SALen-N( H)CH3]CuCl [SALen-N( CHa)z]CuCl [SALen-N( C Z H ~CuCl )~] [SAL~~-N(H)CP,H~] CuCl [SALen-N(H)CH3]CuBr [SALen-N( H)CH3]Cu( CH,COO)a Carbon and hydrogen analysis: Calcd:
111-115 156-157 83-84 181-182 134-1 35 208-210 249-252 165-168 186-188 236-239 224-226 215-218 C, 48.10; H,
-Calcd N
yo--
-----
y
Y
13.05 11.49 14.25 12.56 11.13 9.82 11.73 10,33 11.15 9.83 9.17 8.07 23.02 10.13 21.90 9.66 19.99 8.80 18.79 8.28 19.20 8.75 21.18 9.34 5.34. Found: C, 48.83;
AND
12.86 12.24 11.08 10.40 25.01
Cu
-Found 70N
12.98 14.34 11.01 11.46 11.02 9.34 23.10 22.32 20.10 18.88 19.09 21.00
11.25 12.82 9.86 10.47 9.81 7.99 10.03 9.60 8.69 8.41 8.84 9.36
--Y
12.81 12.17 10.94 10.50 25.01
H , 5.58.
as the p nitrogen has a very small donor power because of the electronic and steric properties of the phenyl group. The dipole moment in benzene solution is 2.20 D. (see Table 11) for both of the copper complexes. TABLE I1 DIELECTRIC POLARIZATION DATAFOR SOME [SALen-N(R)R']zCuII COMPLEXES IN BENZENE AT 25" R
CHI CHI C6H5
R'
CH3 C6H6 CBHS
Pzm, cc
RD,
Po,
cc
cc
343 300 346
128 165 204
189 102 100
P,
u.
3.03 2.23 2.20
This value is high with respect to the values of 1.20 D. for the analogous Ni(I1) complexes1 and of ca. 1.70 D. for the bis(N-n-alkylsalicyla1diminato)copper(11)6 complexes. For the latter compounds i t has been suggested4 that the molecules of the complexes undergo a deformation in solution. The X-ray structure has recently shown that in the solid state the bis(N-ethylsalicylaldiminato)copper(II) complex has a structure which is intermediate between trans planar and tetrahedral.' The dipole moment of 2.20 D. probably only indicates a greater distortion from the trans-planar configuration. The relatively high intensity of the absorption band a t cu. 16,500 cm-I for these two complexes ( E 120 and 150 in CHC18) can be interpreted as due to this distortion.8 The absorption spectra of [SALen-N(H) C B H ~ ] ~ C and U I ' [5-Cl-SALenN (C2H&,]2Cu1' are also indicative of a trans-planar configuration. It is interesting to note that the ligand 5-Cl-SALen-N(CzH& gives rise to pentacoordinate structures with Ni(II)2 and C O ( I I ) ~because the steric hindrance, due to the two ethyl groups linked to the /3 nitrogen, opposes six-coordination. The reflectance spectra of [5-CI-SALen-N (H)CHS]2Cu1' and [SALen-N(CH3)2]2CuI1 are different from those of the preceding compounds. The absorption maximum is displaced to lower energies from ca. 18,500 to 13,300 cm-l. These spectra show strong similarities (Figure 1) to the spectrum of the bis(N-
methylsalicylaldiminato)copper(II) which exhibits a trigonal-bipyramidal configurationg when i t is guest in the lattice of the zinc analog and to the spectrum of the bis(sa1icylidene-y-iminopropyl)aminecopper(II) complex which has a distorted trigonal-bipyramidal configuration.1° The infrared spectrum of the -N(H)CHS complex shows two bands in the region of N-H stretching frequencies: one weak and sharp a t 3300 cm-l and the other medium and broad a t 3125 cm-l. The frequency of the first band and its features are characteristic of the N-H stretching of a secondary amine completely free of further bonds. The large shift of the second band cannot be explained by assuming only a Cu-NH coordination bond.
(6) L. Sacconi, M. Ciampolini, F. Maggio, and G. Del Re, J . A m . Chem. Soc., 82, 815 (1960). ( 7 ) C. Panattoni, private communication. (8) R. L. Belford and T. S. Piper, Mol. P k y s . , 6 , 251 (1962).
(9) L. Sacconi, M. Ciampolini, and G. P. Speroni, J . A m . Ckem. Soc., 87, 3102 (1965). (10) L. Sacconi and I. Bertini, ibid., in press.
5
10
15
20
Frequency, c r n - ' ~ l O - ~
Figure 1.-Diffuse reflectance spectra of (A) [SALenN(CH3)z]2C~11, (B) bis(sa1icylidene-y-iminopropy1)aminecopper(11),(C) bis(N-methylsalicyla1diminato)copper(11).
1522 L. SACCONI AND I. BERTINI Furthermore, the shape of this band is indicative of a hydrogen bond. The difference between the two N-H groups present in the molecule might be explained by the fact that only one /3 nitrogen is linked t o the copper atom so that the complex has a pentacoordinate structure of the type of [5-Cl-SALen-N(CzHj)2]2NiI1.l1 I n this case, the hydrogen bond would be intramolecular and involve the oxygen of the other coordinated salicylaldimine group. The acceptance of a pentacoordinate structure could also account for the shift of the absorption band in the reflectance spectrum to a lower frequency. It is known for instance that adding ammonia to a C U ( N H ~ ) ~ solution ~+ to form Cu(NH3)b2+ causes a lowering of the frequency of the absorption rnaximum.l2 The possibility of an octahedral structure of the type of the analogous Ni(I1) and Co(I1) complexes seems less probable. In fact the octahedral coordination could not give a reasonable explanation of the splitting of the N-H stretching bands of the N(H)CH3 compound. The absorption spectra of both the N(H)CH3 and N(CH3)n complexes in benzene solution indicate the existence of an equilibrium between the trans-planar and probably pentacoordinate forms, the proportion in the planar form being very high a t room temperature. The rather high value of 3.03 D. a t 20’ for the dipole moment of [SALen-N (CH& ]2CuI1 in benzene solution supports this hypothesis. Series 11: [SALen-N(R)R’]CuY (Y = C1, Br, CH3COO).-All of the ligands of the complexes studied here, except those with R = CH3 or C6Hb and R’ = C s H ~ tend , to behave as tridentate. This is because the electron-releasing effect of the groups R , R’ confers an increased donor strength to the /3 nitrogen. The donor capacity of the /3 nitrogen increases depending on the substituents R , R’ in the following order :lt2 N(H) CsHj, N(CzHj)2, N(CH3)zr N(H)CH3. The tendency of these ligands to function as tridentate, together with the tendency of Cu(I1) to give squareplanar complexes, ensures that, if the preparation of the complexes of series I is conducted in the presence of C1- ions, tetracoordinate planar complexes of the general formula [SALen-N(R)R’]CuCl are formed. I n these complexes the copper atom is coordinated t o only one Schiff base, which behaves tridentately, and the fourth coordination position is occupied by the halogen. These compounds are obtained by allowing CuClz to react with the respective Schiff base in alcohol. Moreover, even in the absence of C1- ions, the same products are obtained by mixing the appropriate amines with the bis(salicylaldehydate)copper(II) complex in chlorine-containing solvents such as CHC& or CCl,. (11) L. Sacconi, P. L. Orioli, and M. Di Vaira, J . A m . Chewz. Soc., 87, 2059 (1965). (12) C. K. Jirgensen, “Absorption Spectra and Chemical Bonding in Complexes,” Pergamon Press Inc., h-ew York, N. Y., 1952, p 125.
Inorganic Chemistry
Figure 2.-Diffuse
reflectance spectra of some [SALen-N(R)R CuCl complexes.
’1 -
Finally, if complexes of series I are dissolved in CHC13 or CCl, and are heated a t reflux for a short time, the chlorine-containing products of formula I1 are again obtained. The formation of the complexes therefore involves dehalogenation of the solvents. Attempts to prepare complexes of series I1 with ligands which behave as bidentates were unsuccessful. By reaction of CuBrzor Cu(CH3C00)2with Schiff bases, compounds in which the fourth coordination position is occupied by a bromine or acetate ion are obtained. The reflectance spectra of the chloro complexes indicate that they are square-planar. It should be noted (Figure 2) that the absorption band is displaced toward lower energies with the increasing substitution on the /3 nitrogen, as a function of the nature of the R and R’ substituents according to the order given above. This order for the spectrochemical series is in accordance with that found by MeekI3 for octahedral complexes of Ni(I1) with N-alkyl-substituted ethylenediamines. It is also in accordance with the series of the donor strength of the amine toward the acceptor with respect to bis (benzoylhydrazone)nickel(II).l 4 Acknowledgment.-Thanks are expressed to Dr. J. Gelsomini for microanalyses and to Mr. F. Zanobini for assisting in the preparation of compounds. Financial support from the Italian C.N.R. is gratefully acknowledged. (13) S. F. Pavkovic and D. W. Meek, Inoig. Chem , 4, 20 (1965). (14) L. Sacconi, G. Lombardo, and P. Paoletti, J . Chem. Soc., 848 (1958).
